Amplitude control unit



Dec. 6, 1955 L. HIMMEL AMPLITUDE CONTROL UNIT Filed Aug. 9, 1951 R E SOURC E RE SOURCE lNVENTOR LEON H/MMEL BY fl ATTORNEY United States Patent AMPLITUDE CONTROL UNIT Leon Himmel, Cedar Grove, N. 1., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Application August 9, 1951, Serial No. 241,122

6 Claims. (Cl. 333-7) This invention relates to radio frequency energy distribution systems and more particularly to the amplitude control feature thereof.

In instrument landing systems and radio beacons for guiding aircraft, it is desirable to provide devices for controlling the amplitude level of the signal modulated radio frequency energy at certain associated antennas. One of the difiiculties is to provide such control without altering the phase of the energy. An object of this invention, therefore, is to provide an amplitude control unit which may be adjusted for selected amplitude distribution of signal energy between two loads without affecting the phase relation of the energy at the loads.

A feature of the invention is the simplicity of the control unit. By employing a bridge circuit with loads connected to two diagonal junctions and supplying radio frequency energy to the other two diagonal junctions, one leg of a quarter wavelength bridge being provided with a transposition or of a length one-half wave length greater than the quarter wave lengths of the other three legs, the signal energy may be applied therethrough to the loads at desired amplitude level relationship without altering the phase relationship of energy supplied to the loads. This supply of radio frequency energy to the bridge is done through a phase changer having two phase changing portions, one for each side of the bridge. Altering the phase shift of the two portions simultaneously and in opposite equal amounts the currents supplied to the bridge, results in current output to the loads varying in amplitude according to the adjustment of the phase changer, but without alteration of the phase relationship of the energy at the loads.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic illustration of an amplitude control unit in accordance with the principles of this invention;

Figs. 2 and 3 are vector diagrams used in explaining the operation of the amplitude control unit;

Fig. 4 is an alternative form of phase changer that may be used in the control unit;

Fig. 5 is a view in side elevation of another phase changer that may be used in the control unit; and

Fig. 6 .is a cross-sectional view taken along line 6-6 of Fig. 6.

Referring to Fig. 1, the amplitude control unit comprises a source of radio frequency energy 1 and a phase changing device 2, whereby radio frequency energy may be supplied with controlled phase to a bridge circuit. The phase changer 2 comprises a conductor having a loop or cavity 3 with which a probe 4 is in coupled relation. The bridge circuit 5 to which the phased energy is supplied, is provided with two loads 6 and 7 connected to two diagonal junctions 8 and 9, while the phased input energy is fed to the other two diagonal junctions 10 and 11 by means of transmission lines 12 and 13. The bridge comprises three quarter wavelength legs 14, 15, and 16 and one three-quarter wavelength leg 17. The legs are made up of coaxial lines. The three-quarter wavelength leg 17 provides the equivalent of the usual transposition, this leg being one-half wavelength longer than the one-quarter wavelength legs 14, 15, and 16.

It will be noted that energy supplied at loads 6 and 7 through arms 15. and 14 is also cophasal while energy supplied to these loads through arms 16 and 17 is always antiphasal. Thus a phase relation between energy at loads 6 and 7 is maintained for all adjustments of phase shifter 2.

Referring to the vector diagrams of Figs. 2 and 3, and assuming that I1 and I2 are the currents supplied to the two junctions 10 and 11, the current distribution may be represented by vectors I16 and 126 to the load 6 and I17 and 127 to the load 7. These vectors may be represented as shown in Fig. 2, the vectors I16, I26, and 117 being in phase while the vector I27 is out of phase. This represents the condition when the phase changer portions of 3 as determined by the position of 4 are equal. The vectors I16 and I26, Fig. 3, add to deliver the current sum to the load 6. The current vectors I17 and I27 subtract with the current difference delivered to the load 7. As the phase angle is simultaneously shortened and lengthened by corresponding amounts for I1 and 12, the condition will change as illustrated in Fig. 3. From Fig. 3 it can be seen that both of the current vectors I15 and he vary in amplitude but that they maintain a constant phase relation. The vector sum of the currents I1 and I2 is thus delivered to the load 6 and the vector difference is delivered to load 7. Since it is the function of a bridge to isolate the two load inputs, the currents I1 and I2 are applied to loads of constant impedance, and hence will be constant themselves. The total input impedance is thus a constant. Various forms of impedance matching may be used to satisfy the input impedance requirements of the system with which the amplitude control unit is associated. Either a balanced or coaxial line may be used with a suitably balanced bridge. As shown in Fig. 1, the bridge comprises a coaxial form and the phase changer 2 comprises a single motion control such as probe 4 whereby one line is lengthened and the other is shortened simultaneously.

In Fig. 4 a form of movable phase adjuster is shown comprising a coaxial line comprising outer and inner conductors 18 and 19 in two separated sections positioned for telescoping relation with a bridging coaxial transmission line permanently connected to line 20 from radio frequency source 1. The opposite ends of the line 18, 19 may be connected to the junctions 10 and 11 of the bridge shown in Fig. 1. The inner telescoping coaxial structure to which line 20 is connected, comprises an outer conductor 21 and an inner conductor 22, the ends of each being provided with brushes or other sliding contacts 23 and 24 for sliding engagement in a telescoping fashion with respect to the inner and outer conductors 18 and 19. By moving the Y coupler represented by structure 21, 22 and line 20 to the right or left as viewed in Fig.5, the phase of the currents applied to the bridge are varied simultaneously and in opposite relation whereby a corresponding amplitude variation is obtained at the outputs of the bridge.

Figs. 5 and 6 show another phase changer comprising parallel conductors 25 and 26 disposed in a semi-circle on opposite sides of a rotating conductor; a sector of which is provided with a layer of dielectric 28. The lines 25 and 26 are fed over lines 29 and 30. As the rotor is moved relative to the parallel lines the effect is similar to moving a probe along the parallel lines. The movement of the dielectric between the parallel lines thus produces a phase change in the output ends of the parallel line system which is complementary for the two sides of the bridge.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made by way of example only and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. An amplitude control unit for varying the amplitude of the output radio frequency energy while maintaining constant the phase of said output energy and constant impedance to the source of radio frequency energy comprising a bridge circuit the legs of which comprise transmission lines with the legs so proportioned in length that one leg thereof is the equivalent of a three-quarter wavelength leg as compared to a quarter wavelength for the other three legs, output means for connecting two loads at two diagonal junctions of the bridge, a source of radio frequency energy, means including two conductive paths to apply said energy to the other two diagonal junctions of the bridge and means to vary simultaneously and in complementary relation the electrical length of said two conductive paths.

2. An amplitude control unit according to claim 1, wherein the phase changing means includes a phase changing structure divided substantially equally between two portions coupled respectively to said two paths, one

portion controlling the phase of energy to one side of the bridge and the other portion controlling the phase of energy to the other side of the bridge, and means for adjusting the phase changing structure to simultaneously lengthen one phasing portion and shorten correspondingly the other phasing portion.

3. An amplitude control unit according to claim 1, wherein the means for changing the phase includes a conductor having an arcuate configuration with the ends thereof coupled respectively to said two paths, and a probe coupled to said source, said probe being disposed for adjustment along said arcuate conductor.

4. An amplitude control unit acording to claim 1, wherein said two paths comprise coaxial lines and the phase changing means includes a coaxial structure having brushes at the ends of the inner and outer conductors thereof for sliding telescoping relation respectively with the inner and outer conductors of said two coaxial lines, and means coupling energy from said source to said coaxial structure.

5. An amplitude control unit according to claim 1, wherein the phase changer comprises a parallel line circuit coupled between said two conductive paths, means for feeding said circuit from said source and a rotor disposed between said lines with a sector of conductive material adapted to determine the impedance relationship of said parallel circuit as said sector is moved therealong.

6. An amplitude control unit for varying the amplitude of the output radio frequency energy while maintaining constant the phase of said output energy and constant impedance to the source of radio frequency energy, comprising a bridge circuit having one leg thereof arranged to obtain an equivalent of a three-quarter wavelength leg as compared to a quarter wavelength for the other three legs, output means for connecting two loads at two diagonal junctions of the bridge, a source of radio frequency energy, first and second coaxial lines coupled to the other two diagonal junctions of said bridge, a Y coupler of coaxial line construction coupling said source to said first and second lines in parallel, and means for adjustably telescoping said Y coupler in a complementary manner with respect to said first and second lines, whereby the length of the line connections between said source and said two other junctions are variable in complementary relation.

References Cited in the file of this patent UNITED STATES PATENTS 2,095,758 Mabry Oct. 12, 1937 2,409,449 Sanders Oct. 15, 1946 2,414,431 Alford Jan. 21, 1947 2,437,067 Bingley Mar. 2, 1948 2,461,832 Meacham Feb. 15, 1949 2,543,827 Brown Mar. 6, 1951 2,544,842 Lawson Mar. 13, 1951 

